1. Field of the Invention
The present invention relates generally to a system for reducing mechanical loss of an internal combustion engine and particularly to a system for reducing pumping loss of an internal combustion engine by operating the engine during low load operating period thereof similarly to high load operations of an internal combustion engine having a stroke volume smaller than that of the former engine.
2. Description of the Prior Art
As is well known in the art, Otto cycle engines are incapable of transforming all of heat energy produced in combustion chambers thereof to shaft output and a fair portion of the heat energy is lost as various kinds of losses to cause decreases in thermal and mechanical efficiencies and to preclude an endeavor to make improvement in fuel economy.
As one of mechanical losses of the engine, there is pumping loss which takes place in the intake and exhaust strokes of the engine. A usual pumping loss is represented by the area surrounded by the line O-a-1-4-O in a Pressure-Volume diagram shown in FIG. 1 of the accompanying drawings. The pumping loss is greater during engine low load operating period rather than during engine high load operating period. For this reason, an automobile engine more used at low and medium loads is inferior in fuel consumption than an automobile engine more used at high loads.
Generally, when an engine equipped in an automobile is replaced by an engine having a stroke volume or capacity smaller than that of the former engine, the fuel consumption is reduced. It is one great reason for this that pumping loss is reduced due to the latter engine being operated at loads higher than those at which the former engine is operated.
Accordingly, if pumping loss is reduced by operating an engine during low load operating period thereof similarly to high load operations of an engine having a stroke volume smaller than that of the former engine without sacrificing characteristics required for high load operations thereof, fuel consumption will be able to be greatly improved or reduced.
This purpose is accomplished by reducing both restricting loss (increases in the suction vacuum) caused by making the degree of opening of a throttle valve of the engine small at the intake stroke and compressing loss caused at the compression stroke during the engine low load operating period. It is necessary for reducing the restricting loss to induct an excessive air-fuel mixture into a combustion chamber of the engine at the intake stroke, while it is necessary for reducing the compressing loss to expel the inducted excessive air-fuel mixture from the combustion chamber at the compression stroke to essentially reduce the swept capacity of the engine. As a solution to this problem, it is considered to greatly delay timing of closing of the intake valve during the engine low load operating period. However, this solution is lacking in the possibility of putting into practice, since it is difficult in mechanism to switch over timing of closing of the intake valve to a predetermined normal value during high load operating period of the engine.